The manner of operation of such a coaxial nozzle consists in injecting into a high-power laser beam passing through said nozzle, one or more materials in powder form, also called hard surfacing materials, carried by a fluid, so as to produce, after melting of the materials, a superficial coating layer on the piece to be treated while assuring an excellent adherence by intimate reflow melting of the surface of said piece, or a surface alloy by deep and controlled reflow melting with the material constituting said piece.
This type of nozzle has a structure permitting the free passage of the laser beam and the supply of materials in the form of powder in a peripheral manner, permitting multi-axial treatments, in the three spatial dimensions.
Nevertheless, the quality of the treatment obtained by means of such a nozzle depends particularly on the quantity and the intrinsic properties of the powder supplied to the incident laser beam and on its interaction with said beam, as well as the shape of the resulting jet at the outlet of the nozzle.
Moreover, the possibility of shaping the jet at the outlet of the nozzle permits, on the one hand, to vary the different parameters of treatment such as the region of application, and the intensity of treatment, the distribution of the particles in the impact zone, etc., and, on the other hand, to increase the calorific output of the operation, by coupling in an optimum way the jet of surface hardening materials with the incident laser beam.
Moreover, at present, the hard surfacing materials are generally injected into the laser beam in an empirical way, without using specific supply devices, nor using means to shape the emitted jet. As a result, a large part of the hard surfacing materials are not irradiated by the incident laser beam and therefore do not take part in the treatment of the resulting surface. Furthermore, the; shape of the jet as well as the distribution of the particles in said jet, depending directly on the injection device for the hard surfacing materials, cannot in any case be controlled.